Recording of sound



March 1, 1938. G. L. DIMMICK 2,109,452

RECORDING OF SOUND Filed Nqv. 2, 1935 E] INVENTOR GAVE/WV L. .aMM/cz BY' ATTORNEY edges perpendicular to the Patented Mar. 1, 1938 UNITED STATES RECORDING OF SOUND Glenn L. Dimmick, Audubon,

N. J., assignor to 1 Radio Corporation of America, a corporation.

of Delaware Application November 2, 1935', Serial No. 47,968 r 9 Claims. (01. 179 100.3)

This invention relates to the recording of sound or the like, and has for its principal object the provision of an improved apparatus and method of operation for obviating certain kinds of distortion which tend to occur in the reproduction of sound from a multiple track or push-pull record such as that disclosed by my copending application Serial No. 674,805, filed June 8, 1933 and assigned to the same assignee as the present application.

As pointed out in the aforesaid copending application, the distortion caused by fogging of the record valleys and under-exposure of the record peaks is avoided by the provision of two similar sound tracks displaced in phase by 189 degrees and arranged to be simultaneously reproduced and combined for operating a loudspeaker or the like. While the types of recorder disclosed by the aforesaid application obviate the distortion mentioned above, their operation sometimes involves the difiiculty that the separate sound tracks tend to overlap at high modulation and are not readily reproduced without distortion when such overlapping occurs. In accordance with the present invention, such distortion of the reproduced sound 1 is minimized or avoided by the provision of means for producing a light beam of such configuration that the two sound tracks are maintained in spaced relationship with one another irrespective of the extent to which they are modulated.

As hereinafter indicated, one suitable means of determining the contour or shape of the light beam is a mask having an aperture provided with a central portion having its edges sloped with respect to a cooperatively associated light slit and with end portions having their opposed or inner light slit and spaced apart to maintain a predetermined spacing between the two record tracks. For convenience of expression, this aperture is sometimes hereinafter designated as having the form of a parallelogram oilset at its opposite ends.

The invention will be better understood from the following description when considered in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

Referring to the drawing,

Fig. l is a diagrammatic showing of a recorder constructed in accordance with the invention,

Fig. 2 illustrates the form of the light beam and its relation to the light slit, and

Fig. 3 illustrates the type of record produced by the recorder.

The recorder includes a light source I from which light passes through a lens II, the aperture l2 of a mask l3 and a lens M to the galvanometer recorder mirror l5 which is vibrated i111 accordance with the signals to be recorded. Light is reflected from the mirror [5 through a lens Hi, the light slit I! of a screen [8 and lenses l9 and 29 to the light sensitive surface of a record strip which is supported upon and moved over the surface of a roller 22.

The image of the aperture mirror i 5 onthe member I 8 l2 reflected by the is indicated at 23.

As will be readily understood, this image is in the form of a parallelogram offset at its opposite ends, is vibrated transversely of the slit and produces two sound tracks 24 and 25 (Fig. 3) which are dis- This form of aperture has the advantage that overshooting of the light beam due to excessive modulation can not cause one of the means operable to vibrate said beam across said slit transversely to said dimension.

record, and means for moving said record transversely of the light transmitted through said slit.

3. A sound recorder of the galvanometer type including means defining a light slit, means for producing a light beam provided with a central across said slit. 4. In an apparatus for producing sound tracks displaced in phase portion, means defining a light slit, and signal responsive means operable to vibrate said beam across said slit.

5. In an apparatus for producing'sound tracks 180 degrees out of phase with one another, the combination of means defining a light slit, means for producing a, light beam having its end portions spaced apart longitudinally of said slit and angularly disposed with respect to its central portion, and signal responsive means operable to vibrate said beam across said slit in a direction parallel to the side edges of said end portions.

6. In a signal recorder including means defining a light slit and signal responsive means operable to vibrate a light beam transversely across said slit, means for producing a light beam having the form of a parallelogram offset to space its ends from one another along the length dimension of said slit.

'7. In a signal recorder including means defining a light slit, signal responsive means operable to vibrate a beam of. light transversely across said slit, a light sensitive record, and means for moving said record transversely of the light transmitted through said slit, means for direct-' ing a beam of light having the form of a parallelogram ofiset to space its ends from one another along the length dimension of said slit to said signal responsive means.

8. In a sound recorder of the galvanometer type including means defining a light slit and means for vibrating a beam of light across said slit, means for producing a light beam provided with a central portion angularly disposed with respect to said slit and with end portions perpendicular to and spaced apart along said slit.

9. In an apparatus for producing sound tracks displaced in phase with respect to one another and including means defining a light slit and signal responsive means operable to vibrate a beam of light across said slit, means for producing a light beam having its end portions spaced apart and angularly disposed with respect to its central portion.

GLENN L. DIMMICK. 

